NtcA is activated by low nitrogen levels, activating HetR. HetR causes the upregulation of het genes, allowing a heterocyst to form. This regulatory process is essential to ensure that heterocysts only form when necessary.
The concentration of NtcA is highest in the middle of 2 heterocysts. This ensures heterocysts form at equal intervals on the filament, helping to maintain a constant concentration of fixed nitrogen in the filament.
The peptide signal PatS is released from heterocysts, inhibiting neighbouring cells from differentiating. It is important to prevent heterocysts from forming too close to other heterocysts, ensuring adequate sucrose can be synthesised by the vegetative cells for the heterocyst.